Combustion engines such as gasoline, diesel or gas engines, as well as the more modern fuel cell systems go through, following the production process, a “running-in” or “hot-test” phase prior to final parts assembly. This running-in phase varies in length from several minutes to a few hours, depending on the type of engine and the operation it will face later on. The “running-in” phase is used to guarantee the functionality of the engine or the system. Today's running-in fluids are quite diverse. They range from pure water over coolant to oil emulsions. Most demonstrate some sort of technical disadvantage.
When putting together the parts after the running-in phase, different means of operation can be used. In many cases, however, the engine builders centralize their production. Following initial testing parts may be shipped all over the world prior to being built into a final operating configuration. During this storage and transport time, the parts may come in contact with corrosive conditions. They require protection against the negative influences faced during storage and/or transport. For economical reasons, the running-in fluid is almost completely removed from the part prior to it going into storage.
This way of operation means that standard coolant formulations do not provide optimal protection to a part following the running-in phase, when it is being stored or transported. Most of the current formulations provide no sustained protection when not in direct contact with the surface they need to protect. Using a standard coolant formulation as hot test fluid is certainly viable in situations where the parts are directly built in after testing. In modern economic climates, however, this is seldom the case. Combined storage and transport time periods have been observed from 3 months to up to 9 months. What is needed is a formulation useful in protecting a part from corrosion following the “running-in” phase and prior to final installation.
In modern combustion engines in particular, thermal loads have high requirements with regard to the materials used. Any form of corrosion, even minor forms, results in a potential risk factor and can lead to a reduction of the lifetime of the engine and correspondingly, safe vehicle operation. In addition, the increased number of different metals and alloys used is increasing, making the system more susceptible to corrosion, particularly on those places where the different parts or alloys make direct or indirect contact with each other.
Corrosion problems increase if transport or storage occurs in cold conditions and freezing point depressants are necessary. Examples of optional freezing point depressants are glycols, small chain organic acids and low molecular weight alcohols. These include but are not limited to ethylene glycol, propylene glycol, diethylene glycol, glycerin and salts of formic acid, salt of acetic acid, salt of propionic acid, salt of adipic acid and glycerol. To be used in cooling systems, they are mixed with water to ensure good heat transfer in addition to freezing protection. Those water based mixtures are however, corrosive under the operating conditions typically found in the targeted applications. Therefore the different metals and corresponding alloys present in the cooling system need to be sufficiently protected from the different corrosion processes like pitting, crevice corrosion, erosion or cavitation.
Oil emulsions can provide protection to parts for a fuel cell system in transit. There are some incompatibility issues which occur when the coolant is added, however. Although the soluble oil provides some residual corrosion protection, it will decrease the heat transfer in engine or fuel cell system by forming a heat isolating, although protective layer. Because efficient heat removal is essential, certainly in the more powerful engines that comply with the more modern environmental legislation, the running-in fluid should not negatively affect the heat transfer from the parts into the cooling system.
Coolants are necessary to remove heat from the engine. To give the engine optimal efficiency, the excess heat must be removed as fast as possible without damaging or decreasing the operation of all cooling system parts. Much work and effort has been expended for the protection of the cooling system materials, especially towards the protection against corrosion at high temperatures. Although from a corrosion standpoint high temperatures can be damaging, there can also be issues at low temperatures during engine operation. At low temperatures, solubility and pumpability can be of concern.
Ideally the coolant remains transparent and free of insolubles. Haziness, precipitation or, in extremes, gel formation are considered detrimental for the performance of an engine coolant. Problems resulting from instability can be seen in damage to water pump seals, engine head seals, hoses or any other parts where softer materials are in use. Gel formation, on the other hand, negatively impacts viscosity, resulting in a decrease in the heat transfer characteristics of the fluid. Heat transfer capability is the main requirement of a coolant fluid. Because the risk for coolant instability is maximized at low temperatures, most problems occur under cold start conditions.
Many antifreeze compositions are known which may contain a variety of ingredients. U.S. Pat. No. 6,802,988, for example discloses an antifreeze concentrate which comprises alkylene glycol in combination with a mixture of at least two dicarboxylic acids or their salts, alkali metal or ammonium molybdates, as well as triazole or thiazole corrosion inhibitors.
U.S. 2002/0030177 A1 discloses a glycol based additive for corrosion prevention further comprising carboxylie acid, azoles, molybdates, polyvinyl, pyrrolidone and a nitrite salt.